The present invention relates to a press die mainly composed of concrete.
Conventionally, a metallic die having abrasion-resistance and shock-resistance has been widely used as a press die.
When manufacturing a metallic die, a blank of the die taken out of a casting mold is provided with a finishing process such as grinding and the like. Thereafter, precision finishing is performed to the contact surface of the processed blank of the die, so as to complete the press die with which a product may be press-molded. However, the above-mentioned steps of manufacturing a metallic die involve large amount of labor and time, and therefore, are not economical.
A concrete material having high strength is now being used as a die material in forming a press mold for steel plates, since it is economically advantageous and may be manufactured in a short time.
However, when forming a press mold using a die formed of concrete material, the sliding of the steel plate is obstructed by the high frictional resistance of the concrete material. As a result, the steel plate has to stretch or extend more than when compared to molding by a die made of cast material. When the steel plate can not extend sufficiently, a crack may occur in the product (steel plate), or a scratch occur in the surface of the product, caused by hard, sharp particles included in the concrete.
Moreover, it is impossible from the characteristics of the concrete material to fill the necessary space of the die with concrete material to repair and improve the abrasiveness of the die.
Therefore, a press die is being developed in which a surface layer is applied to a pressing surface of the concrete material, in order to compensate for the insufficient abrasiveness of the concrete die (refer for example to Japanese Laid-Open Patent Publication No. 8-47732).
Now, a general method of manufacturing a press die made of concrete with a surface layer is explained with reference to FIGS. 8-10.
A. An enclosure 11 is placed around a casting mold 10 which creates the form.
B. A surface material 20 is applied above the casting mold 10 so that is has even thickness.
C. Anchors 21 are placed on the surface material 20, after the surface material 20 has hardened to a predetermined level (half-hardened).
Since the boundary surface (upper surface) of the surface material 20 is smooth unless roughened artificially, the bond with concrete is weak. Therefore, the anchors 21, made of materials having sufficient rigidity and to which the concrete material and the surface layer material cling easily, are placed densely in the surface layer 20, so as to bond the surface material to the concrete to be placed on the surface material, and to prevent exfoliation of the surface material therefrom.
D. Concrete 25 is inpoured to the surface material 20 equipped with anchors 21.
E. An atmospheric pressure steam-curing is performed.
F. The enclosure 11 is removed, and a press die 27 made of concrete to which the surface material 20 is bonded through anchors 21 is taken out of the casting mold 10.
The conventional press die 27 made of concrete has the following drawbacks.
After the surface material 20 and the concrete 25 are bonded, the steam-curing is performed in step E. Since the heat resistance temperature of the surface material is 60xc2x0 C., the curing process is performed under the resistance temperature (60xc2x0 C.), and so the compression strength of the die just after the curing process is low, and it takes time for the die to reach the intrinsic strength of concrete.
Moreover, since the curing process is performed after bonding the surface material 20 to the concrete 25, the difference in contraction between the concrete 25 and the surface material 20 leads to exfoliation of the surface material 20 from the concrete 25.
Even further, when performing a reversing process utilizing a master model, the concrete has to be hardened/cured after reversing the form of the concrete, so the size accuracy of the molding surface due to contraction of the concrete is poor.
The present invention aims at providing a press die made of concrete with improved size accuracy and improved adhesion characteristics of the surface material to the concrete, and a method of manufacturing the same by primarily hardening the base concrete member through steam-curing, and utilizing the aggregate included in the concrete as an anchor when bonding the surface material layer.
The press die made of concrete with a surface layer formed to a pressing surface of a concrete body according to the present invention includes the surface layer formed of synthetic resin bonded to the concrete body utilizing aggregate included in the concrete as the anchor.
Further, the method of manufacturing a press die made of concrete according to the present invention comprises a retardation means mounting step of placing a retardation means on a casting mold for the press die, a concrete filling step of filling an unhardened concrete above said retardation means, a primary hardening step of naturally hardening said concrete, a washing step of washing the portion of the hardened concrete member contacting said retardation means so as to expose aggregate, a secondary hardening step of steam-curing said hardened concrete member, and a surface layer forming step of forming a surface layer on the aggregate exposed surface of the hardened concrete member.
Moreover, the retardation means mounting step includes a step of mounting a means for retarding the hardening of concrete to the pressing surface.
Even further, the surface layer forming step includes steps such as pressing and adhering a surface material on the surface of said hardened concrete, forming said surface layer by inpouring a surface material to the space between the concrete surface and the casting mold for the press die, forming said surface layer by applying a surface material to the concrete surface, and the like.
According to any of the above processes, the surface material constituting the surface layer is bonded to the concrete member utilizing the aggregate comprised in said concrete member as the anchor.